As we now review, the double copy is a map between the dynamics of gauge theory and gravity, where gravity is realized in terms of two copies of a gauge field.
The earliest formulation [1]} of this map takes as its starting point exact solutions which can be written in Kerr-Schild form:
\( g_{\mu \nu } = \eta _{\mu \nu } + \phi k_{\mu } k_{\nu },\) 
